Packet fiber node

ABSTRACT

A packet fiber node is described for use in an access network such as, for example, a cable network. The packet fiber node may differ from convention RF fiber nodes deployed in a cable network in that the packet fiber node is configured to communicate with the Head End of the network using baseband optical signals rather than frequency modulated optical signals. According to a specific embodiment of the present invention, one or more packet fiber nodes may be deployed in a cable network to service a plurality of different subscriber groups which are serviced by a single, conventional RF fiber node.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 09/894,958, filed on Jun. 27, 2001.

BACKGROUND OF THE INVENTION

This invention relates to digital computer network technology. Morespecifically, the present invention relates a new fiber nodeconfiguration to be implemented in cable networks. This applicationincorporates the following applications by reference in their entiretyfor all purposes: U.S. patent application Ser. No. 09/490,761, filed onJan. 24, 2000, U.S. patent application Ser. No. 09/606,503, filed Jun.28, 2000, U.S. Provisional Patent Application Ser. No. 60/159,085, filedon Oct. 13, 1999, and U.S. patent application Ser. No. 09/894,864 filedon Jun. 27, 2001.

Broadband access technologies such as cable, fiber optic, and wirelesshave made rapid progress in recent years. Recently there has been aconvergence of voice and data networks which is due in part to USderegulation of the telecommunications industry. In order to staycompetitive, companies offering broadband access technologies need tosupport voice, video, and other high-bandwidth applications over theirlocal access networks. For networks that use a shared access medium tocommunicate between subscribers and the service provider (e.g., cablenetworks, wireless networks, etc.), providing reliable high-qualityvoice/video communication over such networks is not an easy task.

One type of broadband access technology relates to cable modem networks.A cable modem network or “cable plant” employs cable modems, which arean improvement of conventional PC data modems and provide high speedconnectivity. Cable modems are therefore instrumental in transformingthe cable system into a full service provider of video, voice and datatelecommunications services. Digital data on upstream and downstreamchannels of the cable network is carried over radio frequency (“RF”)carrier signals. Cable modems convert digital data to a modulated RFsignal for upstream transmission and convert downstream RF signal todigital form. The conversion is done at a subscriber's facility. At aCable Modem Termination System (“CMTS”), located at a Head End of thecable network, the conversions are reversed. The CMTS convertsdownstream digital data to a modulated RF signal, which is carried overthe fiber and coaxial lines to the subscriber premises. The cable modemthen demodulates the RF signal and feeds the digital data to a computer.On the return path, the digital data is fed to the cable modem (from anassociated PC for example), which converts it to a modulated RF signal.Once the CMTS receives the upstream RF signal, it demodulates it andtransmits the digital data to an external source.

FIG. 1 shows a block diagram of a conventional cable network 100. Thecable network 100 includes a Head End 102 which provides a communicationinterface between nodes (e.g. cable modems) in the cable network andexternal networks such as, for example, the Internet. The cable modemstypically reside at the subscriber premises 110 a-d.

The Head End 102 is typically connected to one or more hubs 104. Eachhub is configured to service one or more fiber nodes 106 in the cablenetwork. Each fiber node is, in turn, configured to service one or moresubscriber groups 110. Each subscriber group typically comprises about500 to 2000 households. A primary function of the fiber nodes 106 is toprovide an optical-electronic signal interface between the Head End 102and the plurality of cable modems residing at the plurality ofsubscriber groups 110.

Communication between the Head End 102, hub 104, and fiber node 106 a istypically implemented using modulated optical signals which travel overfiber optic cables. More specifically, during the transmission ofmodulated optical signals, multiple optical frequencies are modulatedwith data and transmitted over optical fibers such as, for example,optical fiber links 103 and 105 a,b of FIG. 1, which are typicallyreferred to as “RF fibers”.

As shown in FIG. 1, the modulated optical signals transmitted from theHead End 102 eventually terminate at the fiber node 106 a. The fibernodes maintain the RF modulation while converting from the fiber mediato the coax media and back.

FIG. 2 shows a block diagram of a conventional fiber node 200 such as,for example, fiber node 106 a of FIG. 1. In conventional cable networks,the fiber node 200 is responsible for converting RF modulated wavelengthoptical signals into electrical signals and vice versa. The RF modulatedoptical signals enter the fiber node 200 via downstream RF fiber 205,and are converted into electric signals by the optical-to-electricsignal converter 202. The electrical signals are then amplified bydownstream amplifier 204. The amplified electric signals are then passedto a diplexor 210 which transmits the electric signals over the coaxialline 209 to the plurality of cable modems.

In the reverse direction, the cable modems transmit electrical signalsvia the coaxial line 209 to the fiber node 200. The upstream electricalsignals from the cable modems are received at the diplexor 210, andpassed to the upstream amplifier 206. The upstream electrical signalsare then passed from the amplifier 206 to an electric-to-optical signalconverter, which converts the upstream electric signals into radiofrequency wavelength modulated optical signals which are thentransmitted to the Head End via upstream RF fiber 207.

Typically, the use of RF modulated optical signals in the cable network100 only allows for very narrow opportunities to transmit IP packets.This is because most of the bandwidth of the RF modulated optical signalis used for DOCSIS related signaling between the Head End 102 andplurality of cable modems.

As a result, most conventional cable networks are not equipped to handleincreased data flows relating to new and emerging broadband networkapplications such as video-on-demand, telephony, etc. Accordingly, thereexists a continual need to improve access network configurations inorder to accommodate new and emerging network applications andtechnologies.

SUMMARY OF THE INVENTION

According to different embodiments of the present invention, at leastone packet fiber node may be provided for use in an access network suchas, for example, a cable network. The packet fiber node may differ fromconventional RF fiber nodes deployed in a cable network in that thepacket fiber node is configured to communicate with the Head End of thenetwork using baseband optical signals rather than frequency modulatedoptical signals.

According to a specific embodiment of the present invention, a packetfiber node may include at least one processor, memory, a first interfacefor communicating with the Head End of the access network, and a secondinterface for communicating with at least a portion of network nodes. Inembodiments where the access network corresponds to a cable network, thenetwork nodes will correspond to cable modems. The packet fiber node isconfigured to communicate with the Head End using baseband opticalsignals, and is further configured to communicate with at least aportion of the network nodes using modulated electrical signals. Inaccordance with specific embodiments of the present invention, one ormore packet fiber nodes may be deployed in a cable network to service aplurality of subscriber groups which are serviced by a single,conventional RF fiber node.

An alternate embodiment of the present invention is directed to a packetfiber node which comprises a diplexor, at least one interface, and adistributed cable modem termination system (DCMTS). The packet fibernode may be configured to communicate with the Head End using basebandoptical signals. Additionally, the packet fiber node may be configuredto not include components for communicating with the Head End usingfrequency modulated optical signals. According to a specific embodiment,the packet fiber node may be configured to perform functions relating toDOCSIS MAC scheduling operations and/or functions relating to layer 1and layer 2 protocols.

Another embodiment of the present invention is directed to a method forperforming communication in a cable network. The cable network includesa Head End which communicates with a plurality of different cable modemgroups using at least one upstream channel and at least one downstreamchannel. Spatial reuse of the upstream and/or downstream channelfrequencies may be implemented using at least one packet fiber node.According to a specific embodiment, the same channel frequency may beused to communicate with at least 2 different cable modem groups whichare serviced by a common RF fiber node.

Additional objects, features and advantages of the various aspects ofthe present invention will become apparent from the followingdescription of its preferred embodiments, which description should betaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a conventional cable network 100.

FIG. 2 shows a block diagram of a conventional fiber node 200 such as,for example, fiber node 106 a of FIG. 1.

FIG. 3A shows a specific embodiment of a modified cable network 300.

FIG. 3B shows an alternate embodiment of a modified cable network 350.

FIG. 4 shows the specific embodiment of a modified fiber node 400.

FIG. 5 shows a block diagram of a cable network 500 in accordance with aspecific embodiment of the present invention.

FIG. 6 shows a block diagram of a packet fiber node 600 in accordancewith a specific embodiment of the present invention.

FIG. 7 provides an example of a DCMTS system 700 which may be used toimplement certain aspects of this invention.

FIG. 8 shows a block diagram of a specific embodiment of a Cable ModemTermination System (CMTS) 800 which may be used to implement certainaspects of the present invention.

FIG. 9 shows an alternate embodiment of a cable network 950 which may beused for implementing various aspects of the present invention.

FIG. 10 shows an example of a cable network 1000 implemented inaccordance with a standardized DOCSIS protocol.

DETAILED DESCRIPTION

As the number of cable network subscribers increases, increasedbandwidth demands are continuously being placed upon the cable network.In order to accommodate these increased demands in bandwidth, continualefforts are undertaken to increase bandwidth availability in thenetwork, preferably by utilizing existing infrastructure.

According to different embodiments of the present invention, a pluralityof different techniques are described for providing increased bandwidthavailability to selected nodes in an access network. For example,according to one implementation, a baseband packet-over-fibercommunication system may be implemented for providing increased databandwidth and link budget to network nodes.

As commonly known to one having ordinary skill in the art, basebandoptical signals may be transmitted over an optical fiber at a higherfrequency than RF modulated optical signals. As a result, the availablebandwidth of an optical fiber carrying baseband optical signals may besignificantly greater than the available bandwidth of RF modulatedoptical signals traveling over the same optical fiber. Thus, onesolution for increasing available bandwidth in the cable network is tomodify conventional RF modulated optical communication equipment toinclude additional equipment for performing baseband opticalcommunication.

However, this approach is undesirable since a substantial amount ofinfrastructure supporting RF modulated optical signals has already beeninstalled in most conventional cable networks. Such infrastructure maygenerally be referred to as legacy RF cable network componentry. Thus,rather than converting all existing cable network infrastructure from RFfiber to baseband fiber, a preferred approach for increasing bandwidthavailability in the cable network is to implement a solution which iscompatible with the legacy RF cable network components.

Currently, extensive research is being conducted for arriving at apreferred technique for integrating baseband optical communication withbroadband (e.g. RF modulated) optical communication in a single fibernode which is also configured to support (1) legacy RF downstreams, (2)legacy RF upstreams (3) packet baseband downstream communication, and(4) packet baseband upstream communication. One such technique is shownin FIG. 3A of the drawings.

FIG. 3A shows a specific embodiment of a modified cable network 300. Inthe example of FIG. 3A, the cable network 300 has been configured toenable baseband optical signal communication between the Head End 302and the plurality of fiber nodes 306, in addition to conventionalbroadband communication. Thus, the cable network 300 is configured tosupport both RF modulated optical signals and baseband optical signals.The technique for communicating via baseband optical signals isgenerally known to one having ordinary skill in the art, and isdescribed, for example, in the reference, “Modern Cable TelevisionTechnology,” by James Farmer, David Large, Walter S. Ciciora, MorganKaufman Publishers, Inc., 1999, ISBN: 1558604162, herein incorporated byreference in its entirety for all purposes.

As shown in FIG. 3A, the Head End 302 and hub 304 have each beenmodified to support communication via RF fiber 303 and baseband fiber305. Additionally, as shown in FIG. 3A, each conventional fiber node hasbeen modified to include additional componentry for supporting basebandoptical signal communication. An example of the modified fiber node 306a is shown in FIG. 4 of the drawings.

FIG. 4 shows the specific embodiment of a modified fiber node 400. Inaddition to the conventional fiber node components (402, 404, 406, 408,410) which provide RF modulated optical signal functionality forinterfacing RF fiber with coaxial cable, the modified fiber node 400also includes additional circuitry for providing broadband opticalsignal communication functionality used for interfacing broadband fiberwith conventional coaxial cable. As show in the example of FIG. 4, thebaseband componentry includes a distributed CMTS (DCMTS) 430, upconverter 416, signal combiner 412, and signal splitter 414.

According to a specific embodiment, the functionality of the DCMTS mayinclude all or a portion of the functionality provided by a conventionalCMTS, with the exception that the DCMTS communicates with the Head Endusing baseband optical signals.

According to the embodiment of FIG. 4, the DCMTS 430 is configured toreceive and transmit baseband optical signals via one or more basebandfibers 411. For example, in one embodiment, the DCMTS may use one fiberfor transmitting data, and another fiber for receiving data.Alternatively, a single fiber may be used for both receiving andtransmitting.

One advantage of including a DCMTS in a selected fiber node is that theDCMTS is able to provide additional bandwidth between the Head End 302and that fiber node. Another advantage of including a DCMTS in selectedfiber nodes is that the DCMTS may perform, at a relatively local level,at least a portion of the scheduling or MAC functions typicallyperformed by the CMTS at the Head End (e.g. 302) of the cable network.

For example, according to different embodiments, the DCMTS may beconfigured to perform downstream modulation, upstream demodulation,ranging, registration, generation of channel MAP messages, generationand termination of MAC messages, encryption/decryption, and otherfunctions, such as those, described, for example, with respect to FIGS.7 and 8 of the drawings.

Referring to FIG. 4, downstream baseband optical signals are received atthe DCMTS 430 and passed to up converter 416, where the optical signalsare converted into electrical signals. The electrical signals from upconverter 416 are fed to a combiner 412, which combines signalsoriginating from the baseband fiber with signals originating from the RFfiber. The combined signals are then sent to diplexor 410 where they aretransmitted over the coaxial line 409 to the plurality of cable modemsresiding at the subscriber premises serviced by fiber node 400. Ascommonly known to one having ordinary skill in the art, a primaryfunction of the diplexor 410 is to convert electrical signals from anintermediate frequency (within the fiber node) to a relatively highfrequency (for transmission over the coax cable) and vice versa.

In the reverse direction, electrical signals from the cable modems aretransmitted via coax line 409 to the diplexor 410. The upstream signalsare then passed from the diplexor 410 to the splitter 414. The splitter414 separates the upstream signals, passing a first portion of theupstream signals to the DCMTS 430, and passing a second portion of theupstream signals to the Head End via components 406 and 408. Accordingto a specific embodiment, the DCMTS 430 and CMTS (at the Head End) mayeach receive a copy of the upstream spectrum, and extract desiredsignals from selected portions of the upstream spectrum.

Although modified cable network of FIG. 3A describes one solution forproviding increased bandwidth capacity between the Head End 302 and theplurality of fiber nodes 306, it does not solve the problem of providingincreased bandwidth capacity on coaxial cable lines 309 a and 309 b,which provide the communication paths between the fiber nodes 306 andthe plurality of subscriber groups 310.

One solution for addressing this latter problem of providing increasedbandwidth capacity to the plurality of subscriber groups 310 is toincrease the number of fiber nodes servicing the plurality of subscribergroups. An example of this is shown in FIG. 3B of the drawings.

FIG. 3B shows an alternate embodiment of a modified cable network 350.As shown in FIG. 3B, a different modified fiber node 356 a-d isconfigured to service each respective subscriber group 310 a-d. In thisembodiment, the modified fiber node is pushed deeper into the network,resulting in greater bandwidth availability on each respective coaxcable line connecting a fiber node to its respective subscribergroup(s). For example, if it is assumed that the number of cable modemsserviced by each coaxial fiber 359 a-d is half that serviced by coaxcables 309 a-b of FIG. 3A, then it may be assumed that the availablebandwidth on coax cable lines 359 a-d has effectively doubled.

One problem with the cable network configuration of FIG. 3B is that theprovisioning of additional, modified fiber nodes in the cable networkinfrastructure requires a significant amount of cost and overhead forimplementation. One reason for this expense relates to the cost of themodified fiber node, which must be configured to include RF fibercomponentry as well as baseband fiber componentry.

Another drawback to the configuration of FIG. 3B is that an independentmanufacturer of DCMTS systems would need to install the DCMTS systemsinto conventional fiber nodes, which are typically owned by the cablenetwork service provider. Moreover, in order to manufacture the modifiedfiber node, the independent DCMTS manufacturer would most likely have topartner with fiber node manufacturers, which may include competitors.Additionally, the cable network configuration of FIG. 3B does notprovide the capability for scalable, independent IP networks to be builton top of conventional HFC cable plants containing conventional fibernodes. Thus, it will be appreciated that the cable network configurationof FIG. 3B poses major deployment and business problems for independentDCMTS manufacturers and network service providers.

Additionally, because each conventional fiber node must be modified toinclude a DCMTS and broadband fiber capabilities, deployment of thecable network 350 of FIG. 3B may result in significant servicedisruptions to end users during the modification of the conventionalcable network.

Contrary to efforts in the cable industry to implement a modified fibernode which is capable of supporting both baseband and broadband fiberoptic communication, an alternate embodiment of the present inventiondeparts from conventional wisdom by dividing the problem, whereby twodistinct types of fiber nodes are implemented in the cable network. Thisis shown, for example, in FIG. 5 of the drawings.

FIG. 5 shows a block diagram of a cable network 500 in accordance with aspecific embodiment of the present invention. As show in FIG. 5, thecable network 500 includes two different types of fiber nodes, namely anRF fiber node 506, and a packet fiber node (e.g. 520 a). According to aspecific embodiment, the RF fiber node 506 may include componentry suchas that shown, for example, in fiber node 200 of FIG. 2. The RF fibernode 506 may be configured to handle all legacy RF downstream andupstream communications, and may be configured to perform additionalfunctions associated with conventional fiber nodes.

According to the embodiment of FIG. 5, a baseband fiber network 516 isdeployed which is coupled to the conventional cable network. Thebaseband fiber network may include a plurality of packet fiber nodes520, which are also coupled to the conventional fiber network. In aspecific implementation, the configuration, functionality, andconnectivity of the conventional RF fiber nodes (e.g. 506) are the sameas those in conventional cable networks, such as that shown, forexample, in FIG. 1. However, the packet fiber nodes are pushed deeperinto the network (i.e. closer to the subscriber groups) which, asillustrated in FIG. 5, may result in a plurality of packet fiber nodes520 servicing the subscriber groups (e.g. 510 a, 510 b) which areserviced by a single RF fiber node 506. For example, the RF fiber node506 may be configured to service 500 households past (HHP) while eachpacket fiber node may be configured to service 100 households past,resulting in 5 packet fiber nodes (not shown) servicing the 500households which are serviced by the RF fiber node 506.

FIG. 6 shows a block diagram of a packet fiber node 600 in accordancewith a specific embodiment of the present invention. According to aspecific embodiment, communication with the packet fiber node 600 may beachieved using unmodulated baseband digital signals. In oneimplementation, communication between the Head End and the packet fibernode 600 may be achieved using a plurality of baseband optical signalswhich are simultaneously transmitted on different optical wavelengthsusing DWDM technology. Additionally, according to specific embodiments,the framing of the digital signal may be, for example, Ethernet based,digital frame structures which are based upon Ethernet, or other packetframing mechanisms.

As shown in FIG. 6, the packet fiber node 600 includes a DCMTS 602, anup converter 604, and diplexor 608. According to a specificimplementation, the DCMTS 602 may be configure to perform conversionsbetween packet protocols implemented over the fiber media 613 a, 613 band DOCSIS protocols implemented on the coax media 611.

According to one embodiment, the packet fiber node (e.g. 520 a) may beresponsible for handling baseband communications with the Head End 502and communications for specific DOCSIS channels which are utilized bythe cable modems serviced by the packet fiber node. For example, theDCMTS 602 may be configured to handle layer 1 and layer 2 functionalitysuch as the OSI layer management (e.g. physical layer, RF layer,hardware), MAC layer management, data link layer management, framingfunctionality, DOCSIS protocol functionality, etc. The RF fiber node 506may be responsible for handling legacy RF related signals (such as, forexample, set-top box signals, telemetry signals, etc.) andcommunications which occur on centralized DOCSIS channels.

As shown in FIG. 5, each packet fiber node may be inserted into thecable network 500 using a combiner and/or splitter which may be used toadd and/or separate DOCSIS signals into from the RF lineup. According toa specific implementation, the packet fiber node may be powered from thecoax media to which it is connected. According to alternate embodiments,the packet fiber node may also include a fiber transceiver or(equivalent), a combiner, a power supply, etc. In specific embodimentswhere gigabit interface converters (GBICs) are used, short or long rangeoptics may also be selectively used, as desired.

In the embodiment of FIG. 5, communication between the Head End 502 andthe plurality of fiber nodes 520 may be accomplished via a basebandfiber network 516. According to a specific implementation, one or moreIP tunnels may be formed between the Head End 502 and the plurality ofpacket fiber nodes 520 in order to allow for transmission and receptionof IP packets. In a specific implementation, the IP tunnel(s) may beformed between a CMTS 501 and a DCMTS (residing at one or more packetfiber nodes). The CMTS 501 may be configured to handle layer 3functionality, including packet-related decisions, network layerdecisions, IP related decisions, etc. Additionally, according to aspecific implementation, the CMTS may also be responsible for handingredundancy and/or fail over functionality for selected DCMTS devices.

In addition to being configured to receive baseband optical signals, thepacket fiber nodes 520 may also be configured to receive electricalsignals from the RF fiber nodes via coax lines (e.g. 507A, 507B). Suchelectrical signals may include, for example, clock or other timingreference signals and/or timestamp synchronization signals.

One advantage of creating a separate packet fiber node 600 is that it isless costly and easier to implement than the modified fiber nodedescribed, for example, in FIG. 4 of the drawings. Additionally, by notchanging the connectivity or configuration of the conventional RF fibernodes, implementation of the cable network as shown in FIG. 5, forexample, may be more cost effective and less disruptive in deploymentthan the implementation of the cable network 350 as shown in FIG. 3B ofthe drawings.

Another advantage of the packet fiber node implementation is that thepacket fiber node may be used as a component for deploying fiber to thehome, in the MSO environment. For example, a packet fiber node mayinitially utilize a DCMTS to push the IP layer deep into the network.Thereafter, the DCMTS may be removed, and the packet fiber node may thenbe used as a platform to deliver fiber directly to the home.Additionally, by designing a cable network to include separate packetfiber nodes as shown, for example, in FIG. 5, an independent, scalableIP network may be built on top of any existing HFC network containingany manufacturer's conventional fiber nodes. Thus, the technique of thepresent invention provides a solution to the deployment and businessissues described previously with respect to FIG. 3B of the drawings.Additionally, the packet fiber node solution of the present inventionprovides MSO's with the ability to address high capacity, bandwidth, andcustomer needs without having to upgrade their entire HFC plants to amodified fiber node architecture such as that shown, for example, inFIG. 3B of the drawings.

An additional advantage of the packet fiber node implementation of thepresent invention as shown, for example, in FIG. 5 is that it allows forspatial reuse of downstream and upstream channels from each of the fibernodes to their respective subscriber groups. In contrast, the fibernodes of conventional HFC networks such as those illustrated, forexample, in FIG. 1, are not able to spatially reuse the downstream andupstream channels for communicating with different subscriber groups.

By way of illustration, let us assume that CMTS 120 of FIG. 1communicates with cable modems in Subscriber Group A 110 a via fibernode 106 a and coax line 107 a using a first downstream channel having afrequency of 550 MHz. If different information is to be communicated tocable modems in Subscriber Group B 110 b, CMTS 120 is not able to usethe 550 MHz downstream channel for this purpose since that channelfrequency is already being used to communicate with cable modems inSubscriber Group A. However, referring to FIG. 5, since the packet fibernodes 520 may be configured to include DCMTS devices which handle DOCSISfunctionality, CMTS 501 may communicate with Packet Fiber Nodes A and B(520 a, 520 b) via the baseband fiber network 516, whereupon PacketFiber Node A may then communicate with cable modems in Subscriber GroupA 510 a via coax line 509 a using a downstream frequency of 550 MHz (forexample), and Packet Fiber Node B 520 b may communicate with cablemodems in Subscriber Group B 510 b via coax line 509 b using the samedownstream channel frequency of 550 MHz. Thus it will be appreciatedthat the technique of the present invention allows for the spatial reuseof downstream and upstream channel frequencies for communicating withdifferent subscriber groups which are serviced by a single RF fibernode.

CMTS and DCMTS Configurations

FIG. 7 provides an example of a DCMTS system 700 which may be used toimplement certain aspects of this invention. In the specific embodimentas shown in FIG. 7, a DCMTS 700 provides functions on three networklayers including a physical layer 732, a Media Access Control (MAC)layer 730, and a network layer 744. Generally, the physical layer isresponsible for receiving and transmitting modulated signals over coaxlines to the cable modems. Hardware portions of the physical layerinclude at least one downstream modulator and transmitter 706 and/or atleast one upstream demodulator and receiver 714. The physical layer alsoincludes software 786 for driving the hardware components of thephysical layer.

Electrical upstream data signals (packets) arriving via lines 710 aredemodulated by a receiver 714, and then passed to MAC layer block 730. Aprimary purpose of MAC layer 730 is to encapsulate, with MAC headers,downstream packets and decapsulate, of MAC headers, upstream packets. Inone embodiment, the encapsulation and decapsulation proceed as dictatedby the above-mentioned DOCSIS standard for transmission of data or otherinformation. The MAC headers include addresses to specific modems (ifsent downstream) or to the CMTS (if sent upstream) by a MAC layer block730 in DCMTS 700. Note that the cable modems also include MAC addressingcomponents. In the cable modems, these components encapsulate upstreamdata with a header containing the MAC address of the DCMTS and/or CMTS.

MAC layer block 730 includes a MAC layer hardware portion and a MAClayer software portion. The MAC layer hardware portion includes a MACcontroller 734, and may also include a processor 735. According to aspecific implementation, the processor 735 may be configure to performfunctions relating to MAP routing, load balancing, etc. The MAC layersoftware portion may include software relating to DOCSIS MACfunctionality 784, MAP routing functionality 783 (if desired), loadbalancing functionality 785 (if desired), etc. The MAC layer hardwareand software portions operate together to provide the above-describedfunctionality. In a preferred embodiment, MAC hardware portion 734 isdistinct from a general-purpose microprocessor 755, and is dedicated toperforming some MAC layer functions.

In specific DCMTS configurations, the hardware portions of the physicallayer 732 and MAC layer 730 reside on physical line cards 720 within theDCMTS. The DCMTS may include a plurality of distinct line cards whichservice particular cable modems in the network. Each line card may beconfigured to have its own unique hardware portions of the physicallayer 732 and MAC layer 730.

After MAC layer block 730 has processed the upstream information, it isthen passed to network layer block 744. According to a specificimplementation, the network layer block 744 includes tunneling software782 for causing the upstream information packet to be tunneled to viathe optical fiber interface 702 to the CMTS. According to an alternateembodiment, the DCMTS may be configured to communicate with the Head Endand other DCMTS devices via a standardized IP protocol.

According to a specific embodiment, the optical fiber interface 702 mayalso include a laser and optical-electrical signal conversioncomponentry for converting optical signal into electrical signals andvice-versa. In the specific embodiment of FIG. 7, the optical fiberinterface 702 is configured to communicate with a CMTS (not shown) viabaseband optical fibers 703.

When a packet is received at the optical fiber interface 702 from theCMTS, the network layer 744 passes the packet to MAC layer 730. MACblock 700 then transmits information via a one-way communication mediumto downstream modulator and transmitter 706. Downstream modulator andtransmitter 706 takes the data (or other information) in a packetstructure and converts it to modulated downstream frames, such as MPEGor ATM frames, on the downstream carrier using, for example, QAM64modulation. Other methods of modulation may also be used such as, forexample, QAM256 modulation, CDMA (Code Division Multiple Access), OFDM(Orthogonal Frequency Division Multiplexing), FSK (FREQ Shift Keying),etc. The return data is likewise modulated using, for example, QAM16 orQSPK. According to a specific embodiment, the modulated data isconverted from IF electrical signals to RF electrical signals (orvice-versa) using one or more electrical signal converters (not shown).

Note that alternate embodiments of the DCMTS (not shown) may not includenetwork layer 744. In such embodiments, a DCMTS device may include onlya physical layer and a MAC layer, which are responsible for modifying apacket according to the appropriate standard for transmission ofinformation over a cable modem network. The network layer 744 of thesealternate embodiments of DCMTS devices may be included, for example, aspart of a conventional router for a packet-switched network. In aspecific embodiment, the network layer of the DCMTS is configured as aline card coupled to a standard router that includes the physical layerblock 732 and MAC layer block 730. Using this type of configuration, theDCMTS is able to send and/or receive IP packets to and from the opticalfiber interface 702 using tunneling software block 782. According to analternate embodiment, the DCMTS may be configured to include all or aselected portion of the functionality implemented at a conventionalCMTS. In this latter embodiment, the DCMTS devices may be configured tohandle conventional CMTS functionality, and may be aggregated via arouter or switch at the Head End (illustrated, for example, in FIG. 9).

As shown in FIG. 7, DCMTS 700 includes a central hardware block 750including one or more processors 755 and memory 757. These hardwarecomponents interact with software and other hardware portions of thevarious layers within the DCMTS. They provide general purpose computingpower for much of the software. Memory 757 may include, for example, I/Omemory (e.g. buffers), program memory, shared memory, etc. One or moredata structures used for implementing the technique of the presentinvention may reside in such memory. Hardware block 750 may physicallyreside with the other DCMTS components. In one embodiment, the softwareentities 782, 784, and 786 are implemented as part of a networkoperating system running on hardware 750. According to a specificimplementation, at least a part of the packet fiber node functionalityof this invention are implemented in software as part of the operatingsystem. In FIG. 7, such software may be part of MAC layer software 784and/or the tunneling software 782, or may be closely associatedtherewith. Of course, the packet fiber node logic of the presentinvention could reside in hardware, software, or some combination of thetwo.

According to a specific embodiment, the procedures employed by the DCMTSduring registration and pre-registration are performed at the MAC layerof the DCMTS logic. Thus, in DCMTS 700, most of the registrationoperations would be performed by the hardware and software provided forMAC layer logic 730. Additionally, the operations associated withobtaining an IP address for cable modems may be implemented at thenetwork layer level 744.

In a specific embodiment, the DCMTS systems of this invention may bespecially configured CMTSs or routers such as, for example, speciallyconfigured models in the uBR-7200 series and uBR-10012 series of CMTSsavailable from Cisco Systems, Inc. of San Jose, Calif. In an alternativeembodiment, the invention may be implemented on a general-purposenetwork host machine such as a personal computer or workstation.Further, the invention may be at least partially implemented on a card(e.g., an interface card) for a network device or a general-purposecomputing device.

Although the system shown in FIG. 7 represents one specific DCMTSarchitecture of the present invention, it is by no means the only DCMTSarchitecture on which the present invention can be implemented. Forexample, other types of interfaces and media could also be used with theDCMTS.

Regardless of network device's configuration (for cable plants orotherwise), it may employ one or more memories or memory modules (e.g.,memory 757) configured to store program instructions for the networkoperations and other functions of the present invention describedherein. The program instructions may specify an operating system and oneor more applications, for example. Such memory or memories may also beconfigured to store data structures or other specific non-programinformation described herein.

FIG. 8 shows a block diagram of a specific embodiment of a Cable ModemTermination System (CMTS) 800 which may be used to implement certainaspects of the present invention. According to specific embodiments, allor selected portions of the functionality of the CMTS 800 of FIG. 8 maybe implemented at the distributed CMTS 602 of FIG. 6.

As shown in FIG. 8, the CMTS 800 may comprise a plurality of routingengines (e.g. 801 a, 801 b). In a specific implementation, RoutingEngine A 801 a may be configured as a primary or working routing engine,while Routing Engine B 801 b may be configured as a backup or standbyrouting engine which provides redundancy functionality.

As shown in the embodiment of FIG. 8, each of the routing engines mayinclude a variety of similar modules and/or components. In order toavoid confusion, the various components and/or modules relating toRouting Engine A 801 a will now be described in greater detail with theunderstanding that such descriptions may also be applied to thecorresponding components and modules of Routing Engine B 801 b.

According to a specific embodiment, Routing Engine A may be configuredor designed to include a plurality of functionally different modules orcomponents, including, for example, a Forwarding Processor (FP) Module811 a adapted to provide packet forwarding functionality; a RouteProcessor (RP) Module 803 a adapted to implement routing or forwardingoperations; a utility component 802 a adapted to provide system clockand timestamp functionality; etc. The routing engine components providemay be configured to provide layer one, layer two, layer three and layerfour functionality as well as quality of service (QoS) functionality.

According to a specific implementation, the RP Module 803 a may beconfigured as a processor-based routing system comprising functionalityincorporated within a typical router, such as, for example, speciallyconfigured router models 1600, 2500, 2600, 3600, 4500, 4700, 7200, 7500,10012, and 12000 available from Cisco Systems, Inc. of San Jose, Calif.For example, as shown in the embodiment of FIG. 8, the RP Module 803 acomprises a general-purpose processor 805 a (e.g., a MIPS routeprocessor) coupled to a system controller 809 a and memory 807 a. Itshould be noted that components have been described in singular form forclarity. One skilled in the art would appreciate that multipleprocessors, a variety of memory formats, or multiple system controllers,for example, can be used in this context as well as in other contextswhile falling within the scope of the present invention. The memory 807a may comprise synchronous dynamic random access memory (SDRAM) storagelocations addressable by the processor 805 a for storing softwareprograms and data structures accessed by the components. A networkrouting operating system, portions of which may reside in memory andexecuted by the route processor, functionally organizes the router byinvoking network operations in support of software processes executingon the router.

The RP processor 805 a may be configured to construct and load routingtables used by the FP Module 811 a. The processor 805 a may also beconfigured or designed to perform configuration management functions ofthe routing engine 801 a, and to communicate with neighboring peer,standby, and/or backup routers to exchange protocol data units used toconstruct the routing tables in accordance with conventional routingalgorithms. It will be apparent to those skilled in the art that othermemory types, including various computer readable media, may be used forstoring and executing program instructions pertaining to the operationof the routing engine.

Interface circuitry 827 a may be coupled to the respective interfacecircuitry 833 a, 833 b of line cards 831 a, 831 b. According to aspecific implementation, interface circuitry 827 a may be configured toreside on a backplane logic circuit 823 a of the routing engine. In oneexample, the backplane logic circuit 823 a is embodied as a highperformance, application specific integrated circuit (ASIC). An exampleof a backplane logic circuit that may be advantageously used with thepresent invention is disclosed in co-pending and commonly owned U.S.patent application Ser. No. 09/791,063, filed on Feb. 22, 2001, theentirety of which is hereby incorporated by reference for all purposes.

According to a specific embodiment, the backplane logic circuit (which,according to a specific implementation, may be configured as an ASIC),may be configured to further interface the line cards to a packet buffer825 a and a forwarding engine 821 a of the FP Module 811 a. The packetbuffer 825 a may include memory which is configured to store packets asthe forwarding engine 821 a performs its packet forwarding functions.For example, the packet buffer may be used to store low priority datapackets while high priority, low latency voice packets are forwarded bythe forwarding engine to a data network interface 835 a. According tovarious embodiments, the FP Module 811 may comprise a processor 813 aand memory 815 a for handling transport layer 817 and network layer 819functionality. In one implementation, the processor 813 a may beconfigured to track accounting, port, and billing information forvarious users on a cable modem network 851. The processor 813 a may alsobe configured to maintain desired service flow or session stateinformation in memory 815 a such as, for example, for voice callsinitiated over the cable modem network. The FP Module 811 a may also beconfigured to provide transaction compacting functionality, data parceltunneling functionality, switching functionality, and otherfunctionality described herein.

According to a specific implementation, Routing Engine A 801 a may beconnected to Routing Engine B 801 b via at least one link 846, such as,for example, a backplane line or system bus. Routing engine redundancymay be provided by designating one of the routing engines as the workingor primary routing engine and designating the other routing engine(s) asthe redundant or standby routing engine(s). When configured as a workingrouting engine, the Routing Engine A may perform all appropriateforwarding and routing functions. When a failure occurs at the workingrouting engine, the redundant routing engine (e.g. Routing Engine B) maythen take over the operations of the working routing engine. Thereafter,when Routing Engine A recovers, it may assume the functions of theredundant routing engine, or it may take over the functions of theworking routing engine.

According to different embodiments of the present invention, one or moreof the routing engines may be configured to communicate with a pluralityof line cards (e.g. 831, 835) via point-to-point links. For example, asshown in FIG. 8, each of the plurality of line cards 831 and 835 areconnected to each of the routing engines 801 a, 801 b via point-to-pointlinks 841 and 843. One advantage of the point-to-point linkconfiguration is that it provides additional reliability in that thefailure of one or more line cards will not interfere with communicationsbetween other line cards and the routing engine(s). For example, if LineCard A 831 a suddenly failed, each of the routing engines would still beable to communicate with the other line cards.

According to a specific embodiment, the plurality of line cards mayinclude different types of line cards which have been specificallyconfigured to perform specific functions. For example, Line Card A 831 amay correspond to radio-frequency (RF) line card which has beenconfigured or designed to transmit and receive RF modulated opticalsignals. Line Card B 831 b may correspond to baseband line card whichhas been configured or designed to transmit and receive baseband opticalsignals. Additionally, line cards 835 may correspond to networkinterface cards which have been configured or designed to interface withdifferent types of external networks (e.g. WANs, LANs,) utilizingdifferent types of communication protocols (e.g. Ethernet, Frame Relay,ATM, TCP/IP, etc). For example the data network interface 835 afunctions as an interface component between external data sources andthe cable system. The external data sources transmit data to the datanetwork interface 835 a via, for example, optical fiber, microwave link,satellite link, or through various media. A data network interface mayinclude hardware and software for interfacing to various networks.According to various embodiments, a data network interface may beimplemented on a line card as part of a conventional router for apacket-switched network. Using this type of configuration, the CMTS isable to send and/or receive IP packets to and from the data networkinterface using, for example, network layer software 819 a.

According to a specific implementation, the operations associated withobtaining an IP address for cable modems may be implemented by thenetwork layer software. This may involve the CM communicating with aDHCP server (not shown) via a data network interface, for example.

As shown in FIG. 8, at least a portion of the line cards includesinterface circuitry for providing an appropriate interface between thehost line card, other line cards, and/or the routing engine(s). Forexample, interface circuitry 833 a may include interconnect portscoupled to one or more of the point-to-point links 841, 843. Accordingto a specific implementation, the interface circuitry functions as atranslator that converts conventional formats of data received at theline cards to a suitable protocol format for transmission from the linecard to the appropriate routing engine. In one implementation, theinterface circuitry 833 a may also include circuitry to perform cyclicredundancy code (CRC) generation and checking on packets, along withinterconnect format checking.

According to a specific embodiment, the point-to-point links 841, 843may be configured as clock forwarded links such that each point-to-pointlink comprises at least one data wire for transporting data signals andat least one clock wire for carrying clock signals. However, it will beunderstood to those skilled in the art that the clock forwardingtechnique may be scaled to accommodate other clock forwardingarrangements such as, for example, connections comprising a plurality ordata signals and/or clock signals. Additionally, according to a specificembodiment, each line card may be configured to provide at least onecommunication interface between the routing engines (801 a, 801 b) and aportion of the cable network. The data network interface 835 a maycouple the routing engine 801 a to an external data network 855 such as,for example, the Internet.

According to one embodiment, all or selected lines cards, routingengines and/or data network interfaces may be configured to use at leastone common dedicated line or backplane (e.g. 845). According to otherembodiments, the routing engines 801 a, 801 b may have an additionaldedicated connection(s) for supporting redundancy. In a specificimplementation, the backplane may be configured as an Ethernet mediumthat is shared by the CMTS. When the line cards are inserted into thebackplane, they communicate with the routing engines over the lines 845in accordance with a “capabilities” exchange that identifies the typesof line cards and their various characteristics/parameters.

According to a specific implementation, during initialization of theCMTS, the routing engines 801 a and 801 b negotiate for working routingengine status over the backplane. Assertion of working status causes theline cards 831 to configure their respective interface circuitry tocommunicate with the designated working routing engine (e.g. RoutingEngine A 801 a). The Routing Engine A 801 a then configures the CMTS andline cards, establishes routing relationships, and initiates trafficforwarding operations. The redundant routing engine 801 b may complete aself-test and perform initialization of its various functions. The tworouting engine assemblies may then exchange conventional negotiationmessages (which may include, for example, health and status messages)via the backplane lines 845. According to a specific implementation, theexchanged messages are defined by an Enhanced High System Availability(EHSA) negotiation algorithm available from Cisco Systems, Inc. of SanJose, Calif. The redundant routing engine may also request transactioninformation from the working routing engine.

When the redundant routing engine 801 b detects that the primary routingengine has failed, the redundant routing engine may take over as the newworking routing engine, and initiate a “cutover” operation to therebycause the line card interface circuitry (e.g. 833 a, 833 b) to identifyand communicate with the new working routing engine 801 b. The newworking routing engine 801 b may then access and retrieve stateinformation (such as, for example, telephone call state information,service flow state information, etc.) stored on selected line cards inorder to maintain existing service flows.

Prior to a failure situation, the redundant routing engine 801 b may beconfigured to monitor the status of the working routing engine 801 a,and may further be configured or designed to receive updatedconfiguration, transaction and/or state information, which may then bestored in an appropriate location in the redundant routing engine 801 b.

The line cards may further comprise circuitry for “looping” packets backonto the redundant routing engine 801 b over the point-to-point links.This allows the redundant routing engine 801 b to send and receive testpackets to evaluate its own operation in addition to the operation ofthe dedicated lines prior to the occurrence of a system failure.

Although the system shown in FIG. 8 represents one specific CMTSarchitecture of the present invention, it is by no means the only CMTSarchitecture on which the present invention can be implemented. Forexample, other types of interfaces and media could also be used with theCMTS. According to different embodiments, the CMTS system of the presentinvention may be implemented as a “routing” CMTS which handles at leastsome routing functions. Alternatively, the CMTS may be a “bridging” CMTSwhich handles only lower-level tasks.

Regardless of the network device's configuration (for cable plants orotherwise), it may employ one or more memories or memory modules (e.g.,memory 807 a, 815 a, etc.) configured to store program instructions forthe network operations and other functions of the present inventiondescribed herein. The program instructions may specify an operatingsystem and one or more applications, for example. Such memory ormemories may also be configured to store data structures, or otherspecific non-program information described herein.

Because such information and program instructions may be employed toimplement the systems/methods described herein, the present inventionrelates to machine-readable media that include program instructions,state information, etc. for performing various operations describedherein. Examples of machine-readable media include, but are not limitedto, magnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD-ROM disks; magneto-optical media such asfloptical disks; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory devices(ROM) and random access memory (RAM). Aspects of the invention may alsobe embodied in a carrier wave travelling over an appropriate medium suchas airwaves, optical lines, electric lines, etc. Examples of programinstructions include both machine code, such as produced by a compiler,and files containing higher level code that may be executed by thecomputer using an interpreter.

It will be appreciated that, according to specific embodiments, thepacket fiber node of the present invention may be implemented in avariety of different cable network configurations. For example,according to one embodiment, as shown, for example, in FIG. 9, the cablenetwork may include a Head End complex which comprises variouscomponents and/or systems such as, for example, a Head End, a super HeadEnd, a hub, a primary hub, a second hub, etc.

FIG. 10 shows an example of a cable network 1000 implemented inaccordance with a standardized DOCSIS protocol such as the well-knownDOCSIS 1.1 RF Interface Specification (document control numberSP-RFIv1.1-I04-000407, Apr. 7, 2000. As illustrated in the example ofFIG. 10, cable network 1000 includes a CMTS 1002, which, for example,may be located at the Head End of the cable network. In at least oneembodiment, the CMTS 1002 includes functionality for performing one ormore of the following operations: service flow management operationsrelating to downstream channel service flow management (e.g., 1007);packet classification operations relating to downstream channelclassification (e.g., 1005); MAC management operations relating to MACmanagement of downstream channels (e.g., 1003); etc.

It will be appreciated that, according to a specific embodiments, atleast a portion of functions described herein which are performed by theDCMTS (e.g., FIG. 7), CMTS (e.g., FIGS. 8, 10), or selected componentsthereof, may be implemented in a centralized CMTS system (e.g. residingthe Head End of the cable network, as shown, for example, in FIG. 5),and/or may be implemented at one or more distributed CMTS (DCMTS)systems (e.g. residing at one or more fiber nodes, as shown, forexample, in FIG. 9). For example, in one embodiment, the DCMTS maypermit the centralized CMTS (at the Head End) to perform a first portionof functions while the DCMTS performs a second portion of functions.

Other Embodiments

FIG. 9 shows an alternate embodiment of a cable network 950 which may beused for implementing various aspects of the present invention. In thecable network of FIG. 9, the centralized CMTS typically residing at theHead End complex 952 has been removed, and its functionalityincorporated into selected DCMTS devices residing in the packet fibernodes 925. Thus, according to the embodiment of FIG. 9, selected DCMTSdevices residing in the packet fiber nodes 925 may be configured toimplement the functions typically implemented by the centralized CMTSdevice, such as, for example, layer 3 functionality and/or at least aportion of the functionality performed by the various logic describedwith respect to FIGS. 7 and 8 of the drawings.

According to a specific embodiment, communication of IP packets betweenthe Head End complex 952 and the plurality of packet fiber nodes 955 maybe accomplished without the use of a tunneling protocol. In such anembodiment, communication between network devices may be accomplishedusing, for example, a standardized IP protocol. Additionally, as shownin the embodiment of FIG. 9, the Head End complex 952 may include aswitch 954 (e.g. Ethernet switch), or other type of traffic handlingdevice which may be configured to route or forward traffic betweennetwork devices in the cable network 950, or between the devices in thecable network and devices in external networks. Further, as shown in theexample of FIG. 9, the Head End complex may also include a DCMTSSynchronization Module 955 which may be configured to providesynchronized clock reference signals and/or synchronized timestampinformation to the plurality of packet fiber nodes 925.

It will be appreciated by one having ordinary skill in the art that thetechnique of the present invention may be implemented in any computernetwork having a standardized protocol for utilizing a centraltermination system (e.g. Head End) to schedule timeslots for remotestations or nodes on a return (or upstream) channel. In wirelessnetworks, the central termination system may be referred to as a HeadEnd or wireless base station. In satellite networks, the centraltermination system may be referred to as a master controlling station.

Although several preferred embodiments of this invention have beendescribed in detail herein with reference to the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments, and that various changes and modifications may beeffected therein by one skilled in the art without departing from thescope of spirit of the invention as defined in the appended claims.

1. A system, comprising: a centralized Cable Modem Termination System(CMTS) component operating between a first network and a second cablenetwork and configured to provide a plurality of cable modems access tothe first network, wherein the centralized CMTS component is configuredto perform a first portion of Data Over Cable Service InterfaceSpecification (DOCSIS) processing on received packet traffic; adistributed node located remotely from the centralized CMTS componentand configured to perform, on communications received from thecentralized CMTS component, a remaining second portion of the DOCSISprocessing not performed by the centralized CMTS component, wherein thedistributed node comprises: a first interface configured to communicatewith the centralized CMTS component; a second interface in communicationwith the first interface and configured to communicate with theplurality of cable modems that are located in the second cable network;circuitry in communication with the first and second interfaces andconfigured to perform the remaining DOCSIS processing, wherein thecircuitry is configured to perform at least one selected from the groupincluding downstream modulation, ranging, registration, generation ofchannel MAP messages, and generation and termination of Media AccessControl (MAC) messages; and the circuitry configured to transfer packetsthrough the first interface and over a portion of the second cablenetwork to the centralized CMTS component; wherein the portion of thesecond cable network is located between the centralized CMTS componentand the distributed node such that the distributed node is remotelylocated with respect to the centralized CMTS component.
 2. The system ofclaim 1 wherein the circuitry is configured to establish one or moreInternet Protocol (IP) tunnels for transferring the communications. 3.The system of claim 1 wherein the communications are passed from thecentralized CMTS to the distributed node in digital form and thecircuitry is configured to perform Quadrature Amplitude Modulation (QAM)to format the communications for transmission over a plurality of QAMchannels extending to the cable modems.
 4. The system of claim 1 whereinthe first portion of DOCSIS processing includes a MAC layer operation.5. An apparatus, comprising: a first interface configured to communicatewith a centralized Cable Modem Termination System (CMTS) component of acable network through an Internet Protocol (IP) network; a secondinterface in communication with the first interface and configured tocommunicate with one or more cable modems located in the cable network;circuitry in communication with the first and second interfaces andconfigured to perform, on Data Over Cable Service InterfaceSpecification (DOCSIS)-processed traffic received from the centralizedCMTS component, a selected portion of CMTS functionality that is notperformed by the centralized CMTS component, wherein the apparatusoperates separately from the centralized CMTS and communicates with thecentralized CMTS across the IP network, and wherein the selected portionof the CMTS functionality is quadrature amplitude modulation; thecircuitry configured to transmit the quadrature amplitude modulatedtraffic over Radio Frequency (RF) channels extending to the cable modemsusing the second interface.
 6. The apparatus of claim 5 wherein thetraffic is received over an IP tunnel, and wherein the received trafficis formatted according to DOCSIS Media Access Control (MAC) operationsperformed thereon prior to being received on the first interface.
 7. Theapparatus of claim 5 wherein the circuitry is configured to establish IPtunnels with the centralized CMTS component, the IP tunnels fortransmitting the traffic from the centralized CMTS component to theapparatus.
 8. A system, comprising: a head end component located betweena cable network and an access network, the head end component configuredto perform a first portion of processing on data received over theaccess network, wherein the first portion of the processing includesMedia Access Control (MAC) operations associated with a Data Over CableService Interface Specification (DOCSIS) protocol; a node locatedremotely with respect to the head end component and a plurality of cablemodems of the cable network, the node configured to perform a secondportion of the processing on the data from the head end component; andthe node configured to transmit the processed data over Radio Frequency(RF) channels extending from the node to the cable modems; wherein thehead end component and the node form a distributed Cable ModemTermination System (CMTS) that extends across the cable network.
 9. Thesystem of claim 8 wherein the node is configured to perform downstreammodulation on the data from the head end component.
 10. The system ofclaim 8 wherein the node is configured to range with the cable modems.11. The system of claim 8 wherein the head end component is configuredto perform packet classification operations relating to downstreamchannel classification.
 12. The system of claim 8 wherein the head endcomponent is configured to conduct MAC management operations relating toMAC management of downstream channels.
 13. The system of claim 8 whereinthe data is transmitted from the head end component to the node in adigital form and is not modulated for RE transmission.
 14. The system ofclaim 8 wherein the node is configured to register the cable modems. 15.The system of claim 8 wherein the node is configured to generate channelMAP messages.
 16. A system, comprising: a distributed node configured tocommunicate with a centralized Cable Modem Termination System (CMTS)component that operates between a first network and a second cablenetwork and provides a plurality of cable modems access to the firstnetwork from the second cable network; wherein, when operating, thedistributed node forms a distributed CMTS with the centralized CMTScomponent; the distributed node configured to receive, from thecentralized CMTS component, packet traffic that has been partially DataOver Cable Service Interface Specification (DOCSIS)-processed by thecentralized CMTS component; the distributed node configured to perform,on the received packet traffic, a remaining portion of the DOCSISprocessing, wherein the remaining DOCSIS processing includes quardratureamplitude modulation; and the distributed node configured to transmitthe quadrature amplitude modulated data over Radio Frequency (RF)channels extending from the distributed node to the cable modems. 17.The apparatus of claim 16, wherein the centralized CMTS component isconfigured to perform Media Access Control (MAC) operations associatedwith the DOCSIS protocol on the packet traffic before transmitting thepacket traffic to the distributed node over an Internet Protocol (IP)tunnel.
 18. The apparatus of claim 16, wherein the packet traffic isreceived over an IP tunnel, and wherein the received packet traffic isformatted according to DOCSIS MAC operations performed thereon prior tobeing received by the distributed node.